With the rapid development of the carrier-class Ethernet, the ERP has become an Ethernet service protection method that attracts wide attention in the industry. Based on a physical or logical ring topology, the ERP uses the closed loop and the Ethernet features to implement point-to-point, point-to-multipoint, and multipoint-to-multipoint fast protection switching of services. The ERP is characterized by high utilization ratio of bandwidth, high speed of protection switching, low cost of network construction, and support of point-to-multipoint, and multipoint-to-multipoint service switching.
The Ethernet ring network takes on a ring topology on the physical layer. In order to prevent infinite loop of a packet on the Ethernet ring, a blocked port is set on the link layer. When the service packet passes through the blocked port, the blocked port discards the packet. Generally, the same physical topology may correspond to multiple ring instances, and each ring instance has a corresponding blocked port. A ring instance may correspond to a control Virtual Local Area Network (VLAN) and one or a group of service VLAN(s). It should be noted that the control VLAN is generally used to transmit the control messages of ring instances, and the blocked port does not block the packet and traffic on the control VLAN.
The process of the ERP fault detection and fault recovery is outlined below by reference to accompanying drawings.
FIG. 1 shows an Ethernet ring network in the prior art. As shown in FIG. 1, bridges 1 to 6 serve as nodes to form an Ethernet ring. Port 10 of bridge 1 is a blocked port. Normally, when a service packet passes through the blocked port, the service packet is discarded by the blocked port. The process of fault detection and fault recovery of the Ethernet ring network is detailed below:
1. Fault Detection
The fault detection of the Ethernet ring network is implemented through detection of the ring span. Specifically, Continuity Check (CC) packets are sent periodically to check whether the link between adjacent bridges is normal and to detect faults quickly. If a node fails to receive the CC packet from the adjacent node within a preset period, the link between the node and the adjacent node is determined as faulty.
2. Service Protection in the Case of Faults
After a node detects a fault in the link between the node and its adjacent node, the node blocks the ports at both ends of the faulty link and sends a control message to other nodes on the ring. After receiving the control message, other nodes unblock the normally blocked port, clear the forwarding table, and restart self-learning.
3. Fault Recovery
When a node detects that a fault recovers, the node unblocks the port which is blocked due to link fault, and sends a fault recovery message to other nodes on the ring. After receiving the fault recovery message, other nodes block the normally unblocked port again, clear the forwarding table, and restart self-learning. The Ethernet ring network recovers the normal working state.
The ERP process in the prior art described above reveals that all nodes on the ring clear the forwarding table and restart self-learning once any link fails. In fact, the self-learning may not be necessary in the following circumstances.
FIG. 2 shows a topology of an Ethernet ring network in which the link where the normally blocked port 10 is located fails. As shown in FIG. 2, when faults occur and faults recover on the link between bridge 1 and bridge 2, the faulty link is the link where the normally blocked port is located. After the link fails, the ports on both ends of the link are blocked. The network topology is the same as that before the fault occurs. In this case, the nodes on the Ethernet ring network do not need self-learning because the entries of the forwarding table after self-learning are consistent with those before self-learning.
After the forwarding table of the nodes on the Ethernet ring network is cleared, it is impossible to create a forwarding table again unless self-learning is performed again. In the process of creating a forwarding table, massive broadcast traffic exists on the Ethernet ring network, thus increasing the network load and occupying too many bandwidth resources. Therefore, it may be useful to reduce unnecessary clearing of the forwarding table and self-learning caused by fault occurrence and fault recovery.